Fingerprint imaging system

ABSTRACT

A fingerprint imaging system configured to capture an image of a friction ridge pattern of a subject (e.g., a fingerprint, a palm print, a hand print, a footprint, etc.). The system may include one or more components that reduce the impact of ambient light on the performance of the system. In some implementations, the system may reduce the impact of ambient light without requiring additional power (e.g., to generate an increased amount of radiation) and without including “external” hoods and/or covers designed to block ambient light prior to the ambient light entering system. Instead, the system may reduce the impact of ambient light on performance by blocking ambient light internally within the system along an optical path of radiation used to electronically capture an image of the friction ridge pattern.

FIELD OF THE INVENTION

The invention relates to the reduction of ambient light within afingerprint imaging system configured to electronically capture an imageof a friction ridge pattern of an individual.

BACKGROUND OF THE INVENTION

Fingerprint imaging systems that electronically capture images offriction ridge patterns of individuals are known. However, theperformance of conventional systems may be degraded by ambient lightthat is introduced to the systems during operation. For example, ambientlight may saturate images of the friction ridge in a conventionalsystem. Typically, to address this issue, a fingerprint imaging systemmay include a relatively high-powered light source to overcome theproblem of saturation, and/or external hoods or covers that blockambient light before it enters the system. Each of these solutions isassociated with its own drawbacks. For example, a high-powered lightsource may negatively impact the power budget of the system. Externalhoods or covers may increase the size and/or weight of the system, andmay require additional parts that must be transported in conjunctionwith the system.

SUMMARY

One aspect of the invention relates to a fingerprint imaging system. Thefingerprint imaging system may be configured to capture an image of afriction ridge pattern of a subject (e.g., a fingerprint, a palm print,a hand print, a footprint, etc.). The system may include one or morecomponents that reduce the impact of ambient light on the performance ofthe system. In some implementations, the system may reduce the impact ofambient light without requiring additional power (e.g., to generate anincreased amount of radiation) and without including “external” hoodsand/or covers designed to block ambient light prior to the ambient lightentering system. Instead, the system may reduce the impact of ambientlight on performance by blocking ambient light internally within thesystem along an optical path of radiation used to electronically capturean image of the friction ridge pattern.

In some embodiments, the system includes a platen, a radiation emissionmodule, an image capture device and/or other components. The platen maybe configured to engage the friction ridge pattern of the subject. Theradiation emission module may be configured to provide radiation to theplaten at or near the engagement between the platen and the frictionridge pattern. The radiation may be totally internally reflected at theplaten, with the exception of the locations on the platen where thefriction ridge pattern engages the platen, as total internal reflectionmay be frustrated at these locations. The image capture device may beconfigured to receive the radiation that is totally internally reflectedat the platen and to electronically capture an image of the frictionridge pattern that is engaged with platen.

The system may further include one or more elements that block ambientlight that enters the system before the ambient light reaches the imagecapture device. For example, the system may include a polarizer and anoptical analyzer. The polarizer may include one or more optical elementsconfigured to provide radiation that becomes incident thereon with auniform polarization. This may include transmitting substantially onlythe radiation that becomes incident thereon with the uniformpolarization while blocking (e.g., absorbing, reflecting, etc.)substantially all of the radiation that becomes incident thereon with apolarization other than the uniform polarization. The polarizer may bedisposed within the system between the platen and the image capturedevice to receive substantially any radiation emanating (e.g. viareflection, transmission, etc.) from the platen. This may include bothradiation emitted by the radiation emission module and ambient lightthat enters the system through the platen.

The optical analyzer may include one or more optical elements configuredto transmit only radiation with a requisite polarization. The opticalanalyzer may be disposed within the system between the platen and theimage capture device to shield the image capture device fromsubstantially all of the radiation within the system that does not havethe requisite polarization. The optical analyzer may be formed such thatthe requisite polarization is different than the uniform polarizationthat is imparted to radiation by the polarizer 32. This may effectivelyscreen the image capture device from at least some of the ambient lightthat enters the system through the platen. For example, a beam ofambient light entering the system to become incident on the polarizerand then on the optical analyzer would be polarized by the polarizer andblocked from reaching the image capture device by the optical analyzer,as the polarization imparted to the beam of ambient light by thepolarizer would be different than the requisite polarization.

In some embodiments, the system may include a polarization member andone or more beam folding members. The polarization member may beconfigured to change the polarization of radiation that becomes incidentthereon. In some instances, the polarization member may change thepolarization that becomes incident thereon from the uniform polarizationprovided to radiation by the polarizer to the requisite polarizationthat will be transmitted by the optical analyzer. This may enable someof the radiation that emanates from the platen (e.g., radiation providedby the radiation emission module) to pass through both the polarizer andthe optical analyzer to become incident on image capture device. Thefolding members may be configured to define an optical path from thepolarizer to the polarization member and on to the optical analyzer suchthat radiation that travels along the optical path defined by thefolding members may be transmitted through the optical analyzer. Forexample, the folding members may be disposed within the system to guideradiation that is reflected from the platen at or near the engagementbetween the friction ridge pattern and the platen. This may ensure thatthe radiation from radiation emission module that is reflected from theplaten to form an image of the friction ridge pattern on the platen willbe transmitted through both the polarizer and the analyzer to reach theimage capture device. Other members may also be implemented within thesystem to block ambient light.

One source of ambient light within the system that may be guided by thesystem to pass through to the image capture device includes a beam ofambient light that enters the system through the platen and becomesincident on the radiation emission module. The beam may be reflected bya reflector associated with the radiation emission module back towardthe platen. This beam may then be totally internally reflected by theplaten and proceed along a path similar to radiation emitted by theradiation emission module to become incident on the image capturedevice. In other words, the arrangement of the polarizer, the analyzer,and the polarization member may not be effective in blocking this beamof reflected ambient light because of the proximity (or evencollocation) of the path of this beam with radiation emitted by theradiation emission module. Accordingly, in some embodiments, theradiation emission module may include components designed to preventambient light from entering the system through the platen, becomingincident on the reflector associated with the radiation emission module,and returning back toward the platen from substantially the samedirection as radiation emitted by the radiation emission module.

For example, in some embodiments, the radiation emission module mayinclude a source and a Total Internal Reflection mirror (“TIR mirror”).The source may emit radiation to be guided toward the platen. The TIRmirror may include a surface configured to guide radiation emitted fromthe source toward the platen by total internal reflection. In contrast,a beam of ambient light that enters the system via the platen maypropagate to the TIR mirror with an angle of incidence to the TIR mirrorthat is less than the critical angle of the TIR mirror. Accordingly, thebeam of ambient light may be transmitted through the TIR mirror withoutbeing totally internally reflected. By this mechanism, ambient lightthat would otherwise impact the performance of the system may be dumpedfrom the system through the TIR mirror.

In some other embodiments, the radiation emission module may include asource, a linear polarizer, and a quarter-wave retarder, with thepolarizer and the quarter-wave retarder being disposed between theplaten and the source. The linear polarizer may provide a linearpolarization to radiation that becomes incident thereon. Thequarter-wave retarder may change the polarization of radiation thatbecomes incident thereon. For example, the quarter-wave retarder maychange linearly polarized radiation to circularly polarized radiation,and vice versa.

The arrangement of the linear polarizer and the quarter-wave retarder inthe radiation emission module may reduce the impact of ambient lightthat enters the system through the platen and is reflected from thesource back to the platen. For example, as a beam of ambient lightenters the system through the platen and proceeds toward the source, thebeam of ambient may become incident on the linear polarizer, whichlinearly polarizes the ambient light in a first orientation. Thelinearly polarized ambient light may then become incident on thequarter-wave retarder, which alters the polarization state of ambientlight to make the ambient light circularly polarized. After beingreflected by the source, the ambient light may then again becomeincident on the quarter-wave retarder, which may again change thepolarization state of the ambient light to linear. However, theorientation of the polarization of ambient light after passing throughthe quarter-wave retarder a second time may be orthogonal to theorientation of linear polarization provided to the ambient light by thelinear polarizer. Thus, as the ambient light becomes incident again onthe linear polarizer, the polarization of the ambient light may beorthogonal to the polarization of the linear polarizer, which maythereby block ambient light by virtue of this orthogonality.

These and other objects, features, and characteristics of the presentinvention, as well as the methods of operation and functions of therelated elements of structure and the combination of parts and economiesof manufacture, will become more apparent upon consideration of thefollowing description and the appended claims with reference to theaccompanying drawings, all of which form a part of this specification,wherein like reference numerals designate corresponding parts in thevarious figures. It is to be expressly understood, however, that thedrawings are for the purpose of illustration and description only andare not intended as a definition of the limits of the invention. As usedin the specification and in the claims, the singular form of “a”, “an”,and “the” include plural referents unless the context clearly dictatesotherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a fingerprint imaging system, in accordance with oneor more embodiments of the invention.

FIG. 2 illustrates a radiation emission module for use in a fingerprintimaging system, according to one or more embodiments of the invention.

FIG. 3 illustrates a radiation emission module for use in a fingerprintimaging system, in accordance with one or more embodiments of theinvention.

DETAILED DESCRIPTION

FIG. 1 illustrates a fingerprint imaging system 10, in accordance withone or more embodiments of the invention. System 10 may be configured tocapture an image of a friction ridge pattern of a subject (e.g., afingerprint, a palm print, a hand print, a footprint, etc.). System 10may include one or more components that reduce the impact of ambientlight on system 10. As is discussed further below, system 10 may reducethe impact of ambient light without requiring additional power (e.g., togenerate an increased amount of radiation) or including “external” hoodsand/or covers designed to block ambient light prior to the ambient lightentering system 10. In some embodiments, system 10 includes a platen 12,a radiation emission module 14, an image capture device 16 and/or othercomponents.

Platen 12 may be configured to engage the friction ridge pattern of thesubject. In some embodiments, platen 12 may be provided by a prism 18.Prism 18 may be formed such that radiation is guided to platen 12internally from within prism 18. For example, prism 18 may include alight reception surface 20 through which radiation may be received intoprism 18. Radiation received into prism 18 at light reception surfacemay become incident on platen 12 from within prism 18. This radiationmay be totally internally reflected by platen 12 to be directed towardsa light exit surface 22, from which the reflected radiation exits prism18. Although in FIG. 1 platen 12 is shown as being located at anexternal surface 24 of prism 18, it should be appreciated that one ormore coatings may be applied to external surface 24. In these instances,platen 12 may be formed at the external surface of the outermostcoating. Examples of coatings that may be applied to external surface 24may include silicon oxide, quartz, and/or other coatings.

Radiation emission module 14 may be configured to provide radiation tosystem 10. As is shown in FIG. 1, radiation 26 provided by radiationemission module 14 may be directed to platen 12. For example, radiationemission module 14 may be arranged within system 10 such that radiation26 is emitted by radiation emission module 14 towards light receptionsurface 20 of prism 18 to be directed to platen 12 and totallyinternally reflected at platen 12 toward light exit surface 22.Radiation emission module 14 may include one or more emitters that emitradiation that is directed toward platen 12. The one or more emittersmay include one or more of Organic Light Emitting Diodes (“OLEDs”),lasers (e.g., diode lasers or other laser emitters), Light EmittingDiodes (“LEDs”), Hot Cathode Fluorescent Lamps (“HCFLs”), Cold CathodeFluorescent Lamps (“CCFLs”) incandescent lamps, halogen bulbs, receivedambient light, and/or other electromagnetic radiation emitters.Radiation emission module 14 may include a reflector that directs theradiation emitted from the one or more emitters toward platen 12. Thereflector may include a mirrored surface formed to directionally guidethe emitted radiation in a substantially collimated beam, or thereflector may include another reflective surface that diffuses andguides the radiation (e.g., a white surface). As was mentioned above, atleast a portion of the radiation provided to platen 12 by radiationemission module 14 may become incident upon platen 12 at an angle ofincidence such that the radiation is totally internally reflected atplaten 12 except at locations where the total internal reflection isfrustrated by contact between the friction ridge pattern and platen 12.In some implementations (e.g., as shown in FIGS. 2 and 3 and discussedfurther below), radiation emission module 14 may include componentsdesigned to prevent ambient light from entering system 10 through platen12, becoming incident on the reflector of radiation emission module 14,and returning back toward platen 12 from substantially the samedirection as radiation emitted by the emitters of radiation emissionmodule 14.

Image capture device 16 may be configured to electronically capture animage of the friction ridge pattern that is engaged with platen 12.Image capture device 16 may include, for example, an imaging chip 28configured to generate one or more output signals from which an imageformed on imaging chip 28 may be recreated. For instance, image capturedevice 16 may include one or more CCD chips, one or more CMOS chips,and/or other imaging chips. Image capture device 16 may be arrangedwithin system 10 at an image plane on which an image of platen 12 isformed.

In some embodiments, system 10 may include image forming optics 30.Image forming optics 30 may include one or more optical elementsconfigured to, among other things, form an image of platen 12 on imagecapture device 16. Image forming optics 30 may include one or moreoptical elements designed to reduce the impact of ambient light on theperformance of system 10. These components may reduce the impact ofambient light by, for instance, reducing the amount of ambient lightthat reaches image capture device 16. For example, image forming opticsmay include a polarizer 32 and an optical analyzer 34.

Polarizer 32 may include one or more optical elements configured toprovide radiation that becomes incident thereon with a uniformpolarization. This may include transmitting substantially only theradiation that becomes incident thereon with the uniform polarizationwhile blocking (e.g., absorbing, reflecting, etc.) substantially all ofthe radiation that becomes incident thereon with a polarization otherthan the uniform polarization. Polarizer 32 may be disposed withinsystem 10 between platen 12 and image capture device 16 to receivesubstantially any radiation emanating (e.g. via reflection,transmission, etc.) from platen 12 toward image capture device 16. Inthe implementation illustrated in FIG. 1, polarizer 32 may be disposedto receive substantially all of the radiation that exits prism 18 fromlight exit surface 22. In some embodiments, polarizer 32 may be formedas a separate optical element. In some other embodiments, polarizer 32may be formed as a polarizing film that is disposed onto another opticalelement. For instance, polarizer 32 may be formed as a polarizing filmthat is disposed on light exit surface 22 of prism 18. As anotherexample, polarizer 32 may be formed as a coating on external surface 24of prism 18. As yet another example, polarizer 32 may be formed as anoptical member that is external to platen 12 (e.g., as a hood includingpolarizer 32).

Optical analyzer 34 may include one or more optical elements configuredto transmit only radiation with a requisite polarization. Opticalanalyzer 34 may be disposed within system 10 between platen 12 and imagecapture device 16 to shield image capture device 16 from substantiallyall of the radiation within system 10 that does not have the requisitepolarization. Optical analyzer 34 may be formed such that the requisitepolarization is different than the uniform polarization that is impartedto radiation by polarizer 32. This may effectively screen image capturedevice 16 from at least some of the ambient light that enters system 10through external surface 24 of prism 18. For example, a beam of ambientlight 36 entering prism 18 via external surface 24 and exiting prism 18at light exit surface 22 to become incident on polarizer 32 and thenoptical analyzer 34 would be polarized by polarizer 32 and blocked fromreaching image capture device 16 by optical analyzer 34, as thepolarization imparted to beam 36 by polarizer 32 would be different thanthe requisite polarization. Optical analyzer 34 may be formed as aseparate optical element. In some other instances, optical analyzer 34may be formed as a film that is disposed on another optical element(e.g., imaging lens 42 discussed below).

In some embodiments, image forming optics 30 may include a polarizationmember 38 and one or more beam folding members 40. Polarization member38 may be configured to change the polarization of radiation thatbecomes incident thereon. In some instances, polarization member 38 maychange the polarization that becomes incident thereon from the uniformpolarization provided to radiation by polarizer 32 to the requisitepolarization that will be transmitted by optical analyzer 34. This mayenable some of the radiation that emanates from platen 12 (e.g., beam26) to pass through both polarizer 32 and optical analyzer 34 to becomeincident on image capture device 16. For example, in some embodiments,polarizer 32 imparts a linear polarization to radiation that istransmitted therethrough while optical analyzer 34 transmits onlyradiation with a linear polarization having an orientation that isorthogonal to the linear polarization imparted to radiation by polarizer32. In such embodiments, polarization member 38 may include aquarter-wave retarder (e.g., a quarter-wave plate, a quarter-wave film,etc.) and a reflective surface (e.g., a mirror), with the quarter-waveretarder being disposed at or near a reflective surface, such that theorientation of linearly polarized radiation is shifted by polarizationmember 38 by 90°.

As is shown in FIG. 1, folding members 40 may be configured to define anoptical path from polarizer 32 to polarization member 38 and on tooptical analyzer 34 such that radiation that travels along the opticalpath defined by folding members 40 (e.g., beam 26) may be transmittedthrough optical analyzer 34. Folding members 40 may be disposed withinsystem 10 to guide radiation that emanates from platen 12 along a pathsimilar to radiation 26 that is emitted by radiation emission module 14and reflected at platen 12. This may ensure that radiation 26 fromradiation emission module 14 that forms an image of the friction ridgepattern on platen 12 will be transmitted through both polarizer 32 andanalyzer 34 to reach image capture device 16. Folding members 40 mayinclude one or more mirrored surfaces that reflect radiation. In someother instances, folding members 40 may include one or more otheroptical elements capable of bending or folding an optical path ofradiation.

In some embodiments, image forming optics 30 may include an imaging lens42. Imaging lens 42 may be disposed within system 10 to form an image ofplaten 12 on image capture device 16. Imaging lens 42 may be decenteredand tilted with respect to the optical path defined by image formingoptics 30. This may focus ambient light traveling on a path similar tothe optical path defined by image forming optics 30 onto locations ofimage capture device 16 that are spatially separated from the image ofthe engagement between the friction ridge pattern and platen 12. Forexample, in some instances, a beam of ambient light 44 may enter system10 via platen 12 along an optical path similar to the optical path ofradiation 26 reflected by platen 12 near the engagement between thefriction ridge pattern and platen 12. As may be appreciated from FIG. 1,because of the similarity between the path of beam 44 and the opticalpath of radiation 26, beam 44 may be transmitted through both polarizer32 and analyzer 34 and become incident on image capture device 16.However, if imaging lens 42 is tilted and decentered, beam 44 may beguided by lens 42 to a location on imaging capture device 16 that isspatially apart from the image that is formed of the friction ridgepattern.

It should be appreciated that in some instances imaging lens 42 may beneither tilted nor decentered (as these may impact the aspect of theimage). Further, various properties of other components of system 10 maybe designed to reduce the amount of ambient light that is guided byimage forming optics 30 such that it is transmitted by both polarizer 32and analyzer 34. For example, polarization member 38 and/or foldingmembers 40 may be configured to reduce the amount of ambient light thatis inadvertently guided from polarizer 32 to analyzer by way ofpolarization member 38 (e.g., by virtue of their size, orientation,etc.). In some instances, one or more baffles 46 may be provided withinsystem 10. Baffles 46 may be configured to block ambient light (e.g., abeam of ambient light 48) within system 10.

As was mentioned above, one source of ambient light includes a beam ofambient light 50 that enters system 10 through platen 12 and becomesincident on radiation emission module 14. Beam 50 may be reflected by areflector associated with radiation emission module 14 back towardplaten 12. As should be appreciated from FIG. 1, beam 50 may then bereflected by platen 12 and proceed along a path similar to radiation 26to become incident on image capture device 16. In other words, thearrangement of polarizer 32, analyzer 34, and polarization member 38 maynot be effective in blocking beam 50 because of the proximity (or evencollocation) of the path of beam 50 with radiation 26 emitted byradiation emission module 14. Accordingly, in some embodiments,radiation emission module 14 may include components designed to preventambient light from entering system 10 through platen 12, becomingincident on the reflector associated with radiation emission module 14,and returning back toward platen 12 from substantially the samedirection as radiation emitted by the emitters of radiation emissionmodule 14.

For example, FIG. 2 illustrates radiation emission module 14, accordingto one or more embodiments. Radiation emission module 14, as shown inFIG. 2, is designed to reduce the impact of ambient light that isreflected from radiation emission module 14 back toward platen 12 (e.g.,beam 50 shown in FIG. 1 and described above). Radiation emission module14 may include a source 52 and a TIR mirror 54. Source 52 may includethe emitter that emits radiation and the reflector that guides theradiation emitted by emitter toward platen 12, as was discussed above.TIR mirror 54 may include a surface configured to guide radiationemitted from source 52 toward platen 12 by total internal reflection. Inthe implementation shown in FIG. 2, TIR mirror 54 is formed by aboundary of prism 18, but this is not intended to be limiting. In otherimplementations a waveguide separate from prism 18 may be used to formTIR mirror 54.

TIR mirror 54 is formed such that if radiation becomes incident thereonat an angle of incidence less than a critical angle 56 of TIR mirror 54,then the radiation will pass through TIR mirror 54. If radiation becomesincident upon TIR mirror 54 at an angle of incidence greater thancritical angle 56, then the radiation will be reflected by the opticalphenomenon of total internal reflection by TIR mirror 54. It should beappreciated that critical angle 56 is a function of the indices ofrefraction of the two optical media that come together at TIR mirror 54(e.g., prism 18 and air).

Source 52 may be arranged within system 10 such that radiation 58emitted from source 52 that enters prism 18 via light reception surface20 becomes incident on TIR mirror 54 at an angle of incidence 60 that isgreater than critical angle 56. Accordingly, substantially all of theradiation emitted by source 52 into prism 18 will be reflected at TIRmirror 54 to become incident on platen 12. In contrast, the amount ofambient light that is guided through prism 18 and into source 52 may bereduced. For example, a beam of ambient light 62 may enter prism 18 viaexternal surface 24 and propagate to TIR mirror 54 with an angle ofincidence 64 to TIR mirror that is less than critical angle 56. Beam 62may be transmitted through TIR mirror 54 without being totallyinternally reflected. By this mechanism, ambient light that wouldotherwise impact the performance of system 10 may be dumped from system10 through TIR mirror 54.

FIG. 3 illustrates another example of radiation emission module 14, inaccordance with one or more embodiments. In the implementation shown inFIG. 3, radiation emission module 14 may include source 52, a linearpolarizer 64, and a quarter-wave retarder 66. Linear polarizer 64provides a linear polarization to radiation that becomes incidentthereon. Linear polarizer 64 may be formed as a distinct opticalelement, or linear polarizer 64 may include a linear polarizer film thatis disposed on another optical element within system 10 (e.g., lightreception surface 20 of prism 18). In some embodiments, polarizer 32(shown in FIG. 1 and described above) includes a linear polarizer, andthe orientation of the polarization imparted to radiation by linearpolarizer 64 corresponds to the orientation of the polarization impartedto radiation by polarizer 32. Thus, radiation 68 emitted by source 52that passes through linear polarizer 64 may also pass through polarizer32 after being reflected by platen 12.

Quarter-wave retarder 66 changes the polarization of radiation thatbecomes incident thereon. For example, quarter-wave retarder 66 maychange linearly polarized radiation to circularly polarized radiation,and vice versa. Quarter-wave retarder 66 may be formed as a separateoptical element (e.g., a wave plate), or quarter-wave retarder 66 mayinclude a quarter-wave film disposed on another optical element (e.g.,the reflector of source 52, linear polarizer 64, etc.).

The arrangement of linear polarizer 64 and quarter-wave retarder 66 mayreduce the impact of ambient light that enters system 10 through platen12 and is reflected from source 52. For example, as a beam of ambientlight 70 enters system 10 through platen 12 and proceeds toward source52, beam 70 may become incident on linear polarizer 64 and may therebybecome linearly polarized in a first orientation. The linearly polarizedlight of beam 70 may then become incident on quarter-wave retarder 66,which may alter the polarization state of beam 70 to make the light ofbeam 70 circularly polarized. After being reflected at source 52, beam70 may again become incident on quarter-wave retarder 66, which mayagain change the polarization state of light in beam 70 to linear.However, the orientation of the polarization of beam 70 after passingthrough quarter-wave retarder 66 a second time may be orthogonal to theorientation of linear polarization provided to radiation by linearpolarizer 64. Thus, as beam 70 becomes incident again on linearpolarizer 64, the polarization of the light of beam 70 may be orthogonalto the polarization of linear polarizer 64, which may thereby block beam70 by virtue of this orthogonality.

Although the invention has been described in detail for the purpose ofillustration based on what is currently considered to be the mostpractical and preferred embodiments, it is to be understood that suchdetail is solely for that purpose and that the invention is not limitedto the disclosed embodiments, but, on the contrary, is intended to covermodifications and equivalent arrangements that are within the spirit andscope of the appended claims. For example, it should be understood thatthe present invention contemplates that, to the extent possible, one ormore features of any embodiment can be combined with one or morefeatures of any other embodiment.

1. A fingerprint imaging system configured to capture an image of afriction ridge pattern of a subject, the system comprising: a platenconfigured to engage the friction ridge pattern of the subject; an imagecapture device configured to electronically capture an image of thefriction ridge pattern engaged with the platen; an optical analyzerconfigured to block radiation that becomes incident thereon unless theincident radiation has a requisite polarization, the optical analyzerbeing disposed within the system to shield the image capture device fromreceiving radiation that does not have the requisite polarization,whereby the optical analyzer blocks ambient light without the requisitepolarization that enters the system via the platen and would otherwisebecome incident on the image capture device.
 2. The system of claim 1,further comprising a polarizer disposed such that all, or substantiallyall, radiation emanating from the platen towards the analyzer becomesincident on the polarizer prior to becoming incident on the analyzer,the polarizer being configured to provide a polarization to radiationthat becomes incident thereon that is different than the requisitepolarization.
 3. The system of claim 2, wherein the polarizer isdisposed between the platen and the analyzer.
 4. The system of claim 3,further comprising a polarization member configured to change thepolarization of radiation that becomes incident thereon from thepolarization provided to radiation by the polarizer to the requisitepolarization.
 5. The system of claim 4, further comprising a radiationsource configured to emit radiation towards the platen such that if thefriction ridge is engaged with the platen a portion of the emittedradiation is (i) reflected from areas on the platen at or near theinterface between the friction ridge and the platen, (ii) becomespolarized by the polarizer, (iii) becomes incident on the polarizationmember, (iv) passes through the analyzer, and (v) becomes incident onthe image capture device.
 6. The system of claim 4, wherein thepolarization member comprises a retarder and/or a wave plate.
 7. Thesystem of claim 6, wherein the polarization member comprises aquarter-wave plate.
 8. The system of claim 6, wherein the requisitepolarization is either a circular polarization or a linear polarization.9. The system of claim 1, further comprising a focusing lens configuredto focus an image of the platen and the fingerprint ridge patternengaged therewith onto the image capture device, wherein the focusinglens is decentered with respect to the image capture device, and whereinthe focusing lens is tilted with respect to the image capture device.